The effect of isometric substitute of calcium hydroxide on early stage performance of alkali activated slag concrete(AASC) was investigated. The hydration process of alkali activated slag cement was analysed using hydration kinetics analysis, X ray diffraction and scanning electron microcopy. The results show that the addition of Ca(OH)2 can accelerate the hydration of AASC, leading to a faster slump loss. The acceleration reaction rate constant(K) of alkali activated slag cement increased from 476×10-5 to 560×10-3 and 156×10-2 by addition of 5% and 10%(by mass) Ca(OH)2, which shows that the addition of Ca(OH)2 mainly affects the acceleration period and the hydration induction period is shortened. Simultaneously, the reaction degree(N) decreases from 289 to 126 and 098, which means that the hydration process is controlled by sedimentation of reactant rather than the diffusion controlled process. The hydration process in 24h of alkali activated slag cement is accelerated by adding Ca(OH), with the formation of C2ASH8 and C4AH13.